A WDM network is a network that deploys optical WDM fiber links, where each link carries multiple wavelength channels. WDM, an acronym for Wavelength Division Multiplexing, is a technology that multiplexes multiple signals on a single optical fiber by using optical carriers of different wavelengths using lasers or LEDs. There is a multiplexer and a demultiplexer at each end of the WDM. A multiplexer combines multiple signals at the transmitting end, and a demultiplexer separates the signals at the receiving end. WDM systems are popular in fiber optic networks because they allow expansion by simply upgrading the multiplexers and demultiplexers at each end. And with the help of WDM, no matter how many generations of technology development, we don't need to overhaul the backbone network.

Type of WDM

According to different channel spaces, there are two main types of WDM technologies. One is DWDM and the other is CWDM. DWDM is the abbreviation of Dense Wavelength Division Multiplexing. It is a technology that can concentrate data from different sources on one optical fiber, and each signal is carried simultaneously on its own independent optical wavelength. DWDM has such dense wavelength spacing that it can multiplex more than 80 individual wavelengths or channels of data into an optical stream transmitted over a single fiber. Each channel can carry 2.5Gbps of optical signals, and optical fibers can transmit up to 200 billion bits per second. Therefore, DWDM can maintain a more stable wavelength than CWDM and can be used for long-distance optical transmission. But it is a high-cost device and energy-consuming, not suitable for ordinary people to use.

CWDM (Coarse Wavelength Division Multiplexing) is an economical technology that saves fiber resources by transmitting multiple wavelengths on one fiber. It is a multiplexing technology used in cities and access networks. Transmission is achieved using five or six wavelengths between 1270nm and 1610nm at 20nm intervals. CWDM is a low-cost system because its uncooled modulated laser consumes only 0.5W, and its cost accounts for only 30% of the cost of DWDM. Therefore, CWDM is suitable for applications in short-distance, high-bandwidth and densely populated areas of access points. It can be used in cable television networks where different wavelengths are used for downstream and upstream signals.